Impression material and method for making impression material



Patented Aug. 10, 1937 j PATENT OFFICE ILIPRESSION MATERIAL AND METHODFOR MAKING IMPRESSION MATERIAL Laurence E. Harrison, Prescott,-Ariz.,assignor to Oramold Products Corporation, West Hollywood, Calif., acorporation of Nevada No Drawing. Application October 14, 1935, SerialNo. 44,999

3 Claims.

This invention relates to an impression or molding material suitable foruse by dentists or dental technicians in making impressions of the teethand gums, and which may also be used for '5 other purposes such as themaking of impressions or molds of any desired object in order to permitcastings to be made which accurately reproduce the shape and surfacedetail of such object.

The principal object of the invention is to provide an impressionmaterial having a reversible gel-forming organic hydrocolloid as a baseand adapted for the molding of models from plaster of Paris or the like,provided with a highly ad- 115 vantageous electrolyte material adaptedto hasten the setting of such plaster of Paris upon contact thereof withsuch impression material, which electrolyte material is at the same timeneutral in 7 effect upon the gel-forming hydrocolloid. For 20 this usean alkali-metal sulphate such as potassium sulphate has been found to beparticularly advantageous.

This application is a continuation-in-part of I my co-pendingapplication Serial Number 25 686,251, filed August 22, 1933, issuedNovember 11, 1935, Patent Number 2,021,059.

3 The invention relates more specifically to that type of impressionmaterials having an organic hydrocolloid gel base and which have plastic'3 characteristics when heated or warmed to a temperature somewhat aboveatmospheric temperature, in which plastic condition they may be moldedor pressed into contact with the object to be molded, as in the makingof detailed dental 35 impressions, or the like, and which become setupon chilling below a certain temperature, so as to retain the moldedshape. In the set condition a material of this type is no longersusceptible to plastic deformation but retains. a certain char- 4acteristic of resilience so as to permit it to give or yield when pulledfrom the model, thus, in dental application, permitting the removal ofundercut portions of an impression or inverted Wedges by a resilientnon-plastic deformation of the mate- 45 rial, which deformation isovercome by the natural resilience of the material after removal of thedeforming stress, so that the impression will return or spring back toits original position after it has been removed, whereby perfectreproduc- 50 tion of the original structure may be obtained.

The impression material of the present invention may comprise, for somemolding purposes, merely an aqueous gel such as that obtainable withagar-agar, with the desired water-soluble 55 electrolyte materialdissolved therein, but in general an impression material prepared withagaragar or a like hydrocolloid material is of relatively low mechanicalstrength unless some modifying material is included in the composition.Numerous modifying materials are useful, depending upon the particularuse to which the material is to be put, such as fibrous materials, waxymaterials, resins, et cetera, and in the following specific example of amaterial the modifying agents are to be understood as exemplary only,and the use of the particular type of plasterhardening agent of thepresent disclosure is not to be considered as limited to the specificexample of impression composition.

I may prepare an impression material according to the present inventionby dissolving from 20 to 40 ounces of a gel-forming hydrocolloid, suchas agar-agar, Irish moss, gelatine, or the like, in approximately threegallons of hot water, preferably by boiling, after which from 5 to 9fluid ounces of glycerol may be added. I then prepare a solution of athermoplastic modifying agent such as a thermoplastic rubber isomer of abalatalike type as described in U. S. patent to Fisher, Number1,605,180, by dissolving the same in benzol, carb0ntetrachloride orother suitable solvent. The solvent should have a boiling pointsumciently lower than that of water to permit complete evaporationthereof from the mixture, and the concentration of the solution shouldbe such as to permit spraying or atomization thereof. This solution ofthe modifying agent is then added to the agar-agar solution in suchamount as to provide from one to three per cent of such agent on theweight of water and agar-agar present, and is preferably added slowly,as by spraying or atomizing the solution into a strongly agitated hotagar-agar solution, a very little at a time over a relatively longmixing period. After the introduction of the modifying agent, theheating of the mixture may be continued for such time as to insure thesubstantially complete removal of the solvent.

A suitable amount of a plaster hardening agent is added to the mixture,preferably after mixing of the modifying agent with the agar-agarsolution. Numerous plaster-hardening agents have been previouslysuggested in connection with an impression material having a reversiblegelforming organic hydrocolloid base, such as alum, tannic acid or thelike, but it has been found that these customary plaster-hardeningagents have in some cases a very deleterious effect upon the gel-formingorganic hydrocolloid, particularly if such agent is used in an amountcalculated to give a quite accelerated hardening of the plaster. Theseplaster-hardening agents cause the gel- V forming hydrocolloid topersist in the sol condition at a temperature below the temperature atwhich they normally pass into the gel condition, thus ruining thematerial for impression use. I accordingly prefer to use as aplaster-hardening agent an electrolyte which will not materially alterthe pH value of the sol and which has no deleterious effect on thehydrocolloid material, and I have found that sulphates of the alkalimetals (potassium, sodium, lithium, et cetera) are highly advantageous.For the above mixture, therefore, I prefer to add from 3 to 9 ounces ofan alkali metal sulphate.

In addition to the above ingredients I prefer to add a suitable amountof a satisfactory flavoring material, such as oil of Wintergreen. I alsoprefer to add a small amount of a bactericidal agent, such as menthol,guaiacol or hexyl-re- .sorcinol.

. As a specific example, the proportions of the several ingredients usedmay be as follows:

3 gallons water (390 parts) ounces agar-agar,

7-fiuid ounces glycerol,

8.5" ounces rubber isomer, in the form of a 6% solution in benzol,

6 ounces potassium sulphate,

2 drams oil of Wintergreen,

/2 ounce menthol.

above-mentioned waxes, resins and the like.

During the above-mentioned incorporation of the thermoplastic rubberisomer, considerable water is evaporated from the mixture, and thetemperature maintained during compounding and the duration ofcompounding are preferably so adjusted that the final mixture, startingwith the proportions given in the above specific exam-ple,weighsapproximately 15 pounds and consists substantially as follows:

11 to 12 pounds of water,

30 ounces of agar-agar,

Approximately one-half pound of glycerol,

Three-eighths pound K2804, and

Approximately one-half pound of thermoplastic rubber isomeror othermodifying agent The method of using this material, is in general,similar to the use of impression materials now in common use. Thematerial is preferably softened or rendered plastic by placing aquantity thereof in a suitable container and placing the container incold water, and bringing the water to a boil in about four or fiveminutes. The material may then beremoved from the Water and issuificiently soft and plastic throughout to permit it to be placed inthe usual tray or mold and inserted in the mouth and pressed against theteeth and gums in the usual manner. At the time themate'rial is actuallyinserted in the mouth, the temperature thereof may be about Aftersolidification, the material is nolonger subject to plastic deformationbut may be resiliently deformed for removal so that it will yieldsufficiently to permit undercut, wedged, or dovetailed portions thereofto be easily removed from the mouth and to then spring back to theiroriginal'position. After removal from the mouth, it may be used for thecasting or molding of reproductions in plaster, the presence of theadvantageous plaster-hardening agent serving to effect an acceleratedsetting and hardening of such plaster adjacent the impression surfaces,and thus contributing to the formation of faithful plasterreproductions.

I claim: I f I 1. An impression material comprising an aqueous organichydrocolloid gel base and a plaster-hardening agent consisting of, analkali metal sulphate in aqueous solution therein.

2. The improvement in a process of compounding a plastic composition fortaking impressions and forming molds for plaster casts, of the typecharacterized ,bya base of reversible plastic hydrocolloid whichincludes plaster-set-re'tardant matter, and also including aplaster-set-accelerator; which improvement comprises adding,

the accelerator to the batch substantially at the completion ofcompounding of the batch, thereby minimizing any'efiect of the,accelerator on the composition duringthe process of compounding it.

3. An impression material .comprising an aqueous agar-agar gel base withplaster set-retardant material therein, and also including aplaster-set-accelerator, saidmaterial being more readily plasticiz ableuponheating for use by reason of said accelerator having been addedsubstantially at the completion of compounding of the material, so thateffects of the accelerator upon the composition during compounding have

